The present invention relates generally to mobile concrete batching plants and more particularly to an improved mobile concrete batching and mixing plant comprising multiple units capable of self-erecting assembly on the job site.
Concrete is widely used as a building material and can be brought to a job-site in numerous ways. One of the most common methods is to purchase the concrete from a central ready-mix station, wherein the raw ingredients are placed in a mixing truck and mixed while in transit. Such a system works well and is cost effective when the job site is fairly close to the ready-mix station. However, problems arise when the final location is remote from material storage facilities.
Concrete must be mixed and typically be placed in its final form within an optimum time period. This time period is dependent upon the time of travel from the plant site to the ultimate use location and may vary greatly, depending upon conditions which may be completely out of the control of the operator of the vehicle transporting a desired mix, such as snarled traffic conditions, vehicle breakdown, and the like. Further, material mix ratios calculated for desired hardness of the finished product require differing times for setup and curing to obtain a desired finished hardness. For instance, if over-mixed, excess air becomes entrained in the concrete and will lower the hardened strength. If allowed to sit, the concrete will begin to cure before it is dumped and formed. Additionally, a long hauling distance will translate into high transportation costs.
In construction projects that require a large volume of concrete to be delivered to remote locations, the use of a mobile batch plant is cost effective. A mobile plant typically has many of the same components as a central ready-mix plant, but on a reduced scale. Early mobile plants comprised a number of individual components that were towed to the job site by truck and assembled on location. Such plants could include a mixer unit, thereby eliminating the need to use mixing trucks and allowing the use of more economical flatbed, dump trucks.
A major expense with early mobile plants was the requirement of a crane for assembly on the job site. Cranes were often utilized during assembly and disassembly, but would sit unused for long periods of time in the interim. In response to this problem, self-erecting batch plants were designed.
Early one-piece self-erecting batch plants were limited in their ability to produce large volumes of concrete. Because the entire batch plant was contained within a single unit, the size of the unit was limited to certain maximum road-going weights and dimensions. This also limited the size of the storage bins contained within the unit for aggregate, water and cement.
Another factor to be considered, and often somewhat neglected in design configuration of the unit or units needed to transport a remotely located batching facility, is the consideration of variations in supporting terrain. Obviously, there are very few problems when the terrain is level, as in the case of a surveyed and properly graded area, but this is usually the exceptional case at remotely located sites. The usual new location for road construction is usually unleveled, and may even range from soft, sandy to rocky, and in which variations in ground condition may occur with only a few feet from one another.
A mobile batch plant comprised of multiple units allows for larger volumes of concrete constituents to be initially transported to the job site, and therefore, more concrete to be produced. Each separate unit may be designed and built to maximum weight and dimensions of an entire one-piece prior art batch plant. Providing multiple, individual tractor-trailer rigs allows for a larger batch plant with greater output capacity to safely be transported to the job site.
As stated previously, problems with designing a multiple unit, self-erecting plant has been finding a configuration that would allow stability of the cement tower and a mixing unit during location and erection and use. It is also often desirable to position the cement tower over a conveyor, requiring even increased height. Accordingly, there is a need for a large capacity, self-erecting, mobile concrete batching and mixing plant that utilizes a self-contained stabilizing system that may be transported with one or more components or transporting units, and which may be facilely and quickly assembled along with the self-erecting procedures required during assembly and operation of the cooperating cement tower unit, aggregate transport and supply unit and a mixing unit each of which is attached and conjointly supporting one another.
The present invention is directed to a self-erecting mobile concrete batch plant, wherein three separately transported units may be assembled in the field to become a complete concrete mixing and dispensing station. Each unit comprises a separate trailer, brought to the job site by a semi tractor. The base unit preferably houses and supports aggregate bins, an aggregate conveyor, a large capacity water storage tank and hydraulic and pneumatic motors used to provide power during self-erection and normal operation. The second unit houses and supports the cement batching tower and contains a cement storage bin, a water holding tank and the cement batcher. The third unit contains a mixer, a hydraulically operated tilt pack for the mixer, and an optional dust collection system. All units receive hydraulic power during erection and pneumatic power during operation from the base unit via quick disconnect hoses.
The erection process begins by first locating and positioning the base unit, thereby determining where the finished batch plant will stand, and where the mixed concrete will eventually be dispensed. The base unit is raised off its wheels and leveled and supported by foot pads or plates located at the distal ends of a plurality of hydraulically-operated, extendible support legs. When the base unit reaches the required elevation, hinged outrigger support braces are preferably pivotally moved outwardly to allow placement of the cement tower and lateral support of the base unit during and after erection of the tower unit. The support braces also include hydraulically operated, extendible support legs which will eventually support the cement tower from below.
Next, the cement tower, or silo, trailer unit, with the tower being supported in its prone or supine position on the trailer, is backed into position towards the rear of the previously elevated base unit, and with a bottom portion of the tower extending rearwardly from the end of the trailer until the tower bottom portion abuts the rear of the base unit. Apertured pivot pin supporting clevis members extending from the tower align with corresponding apertured supporting clevis members on the base unit. Pivot pins are placed through the apertures, connecting the two units and forming hinged connections that become the main pivot points for the cement tower during erection. Hydraulically operated, linear actuators, conventionally known as xe2x80x9cramsxe2x80x9d, are anchored to the framework of the tower unit and have the free ends of their respective plungers pivotally anchored supporting clevis members extending from the base unit. The linear actuators are operated to pivotally raise the cement tower to its erect operating position.
The tower rams extend until the tower rotates slightly past the vertical axis. The hinged outrigger support braces are then rotated on their hinges, or pivots, to allow the braces to swing into supporting position beneath the cement tower, or silo. The hydraulically operated legs on the outswung outrigger support braces are then extended to their final location, preferably perpendicular to the base and tower units to aid in supporting the tower from below. The tower""s linear actuators, or rams are then contracted until the tower, or silo, is completely supported by the base unit. The pins are removed from the connection between the linear actuators and the base unit, and the actuators are placed in resting storage positions. The cement batching tower""s removable wheel assembly, left on the ground as the tower was raised, may be moved into storage. The base unit and cement tower are now in their respective final positions. The preferred embodiment of the novel concept utilizes a hinged extension outrigger supporting brace, which may be pivotally moved to provide an articulated, L-shaped brace configuration, with a first portion of the respective braces being directly pivotally supported by the hinge connection with the connected tower and base units, and extending angularly outwardly therefrom, and with the distally extending brace member being pivotally moved relative to a first portion and substantially parallel with the longitudinal plane of the base unit. The final location of each of said braces being dependent upon the supporting elevation of the supporting terrain lying below the respective feet of the brace portions.
The supporting mixer unit may now be positioned longitudinally behind the base unit and cement tower. The mixer unit is not physically connected to the other units, but receives hydraulic power from the base unit during erection. A detachable mixer nose cone, removed for transport, is installed on the mixing drum. Hydraulically operated support legs extend, to raise the mixer unit, and thereby position the mixing drum, which receives and mixes cement paste, aggregate, and admixtures from the other units during operation.
Aggregate storage bins on the base unit hold coarse and fine aggregate, which is delivered to the mixer by the conveyor. The weight of the aggregate is measured by decumulation from the storage bins, as opposed to traditional methods that require a separate aggregate batcher. Cement from the cement bin and water from the holding tank are gravity fed into the cement batcher and mixed into cement paste. The paste is then delivered to the mixer, along with any aggregate admixture from the admixture storage tank. All materials are placed into the rear of the mixer and are initially mixed in the horizontal position.
When the concrete is adequately mixed, the mixer""s stand-alone hydraulic pack tilts the mixer. The concrete is dispensed through the nose cone into a mixing or dump truck for transportation to the final location.